Additions made to FireRed Version & LeafGreen Version from Gold Version, Silver Version & Crystal Version:

All Pokémon up to #386 are compatible with and can be traded to and from FireRed Version & LeafGreen Version.

Improved graphics on par with Ruby Version, Sapphire Version and Emerald Version.

Running shoes

Double Battles

Pokémon Abilities

Pokémon Natures

Other Additions:

Sevii Islands that can be accessed near the end of the game. Three are unlocked after you defeat Blaine, with the last seven being unlocked by defeating the Elite Four. The islands feature some events, Generation II Pokémon that were excluded in Ruby Version, Sapphire Version and Emerald Version, and the Battle Tower.